矩阵中的每一个元素称为像元、像素或图像元素。而g(i, j)代表(i, j)点的灰度值，即亮度值。

由于g (i, j)代表该点图像的光强度（亮度），而光是能量的一种形式，故g (i, j)必须大于零，且为有限值，即： 0＜=g (i, j)＜2n。

用g (i, j)的数值来表示(i, j)位置点上灰度级值的大小，即只反映了黑白灰度的关系。

数字化采样一般是按正方形点阵取样的， -each of the matrix elements known as a pixel, pixels or image elements. And g (i, j), speaking on behalf of (i, j) of the gray values, brightness value. As g (i, j) on behalf of the image point of light intensity (brightness), but just a form of energy, the g (i, j) must be greater than zero, and has limited value, namely : 0 "= g (i, j)" 2n. By g (i, j) to indicate the numerical (i, j) position on the point value of the gray-class size, that is, only reflects the intensity of black and white relations. Digital sampling is usually square lattice sampling,